1. Field of the Invention
The present invention relates to a liquid crystal display, and more particularly to a back light apparatus for use in a liquid crystal display.
2. Description of the Prior Art
A back light module is the key component for liquid crystal display (LCD). By means of the brightness and uniform light source being provided by the backlight module, the LCD panel can display images.
The backlight module can divide into a sidelight mode and a direct light mode according to the position of the light source. The sidelight mode places lamps of the light source on the side edge of a LCD panel and, then, uses a guiding-panel to control light path so that light beams project to a diffuser below the panel and provide uniform light beams. Because of the position of the light source, it suits being used in a light, thin, and power saving display equipment, e.g. a monitor of a notebook. But for big size display and brightness occasions, e.g. TV and desk PC. The sidelight mode cant provide enough brightness. Hence, it needs the direct light mode to directly place the light source below the display panel. The contain space for the light source is bigger, and has a capacity for over two lamps to increase the brightness of the light source and satisfy what's need.
Referring to FIG. 1 and FIG. 2, a direct light back light module 10 comprises a rectangular frame 11 having a container 111, a light source module 12, a diffuser 13, and a supporting rod 14. The surface of the container 111 has a reflection layer 112 to reflect the light beam provided by the light source module 12 to the diffuser 13. The light source module 12 comprises a plurality of light tubes 121 side by side inside the container 111. The two ends of the diffuser 13 fix on a top surface 113 of the rectangular frame 11 and, then, the supporting rod 14 properly is placed on the bottom of the rectangular frame 11, which has one end holding the diffuser 13 to support the diffuser 13.
Due to the supporting rod 14 directly contacting the diffuser 13, the contact part hinders the light from passing. For avoiding the diffuser 13 forming bigger dark area, the supporting rod 14 generally uses a cone having a smaller cross-section on top point and, thus, the top of the supporting rod 14 directly contacts the diffuser 13 with a pointed tip. As the size of the back light module 10 increasing or the inside temperature of the frame 11 raising that causes by the light source module 12, the deformation of the diffuser 13 is increasing and makes downward indentation. Meanwhile, the pointed tip of the supporting rod 14 easily protrudes the diffuser 13 so the diffuser 13 forms a uneven surface or even causes the unequal interval between the diffuser 13 and the light source module 12 such that the diffuser 13 has uneven brightness. The LCD panel display images have light and shade phenomenon. In addition, the supporting rod 14 is placed inside the container 111. As the light source providing light beams impinging onto the surface of the supporting rod 14, the light beams cant effectively reflect or transmissive and, hence, cant project to the surface of the diffuser 13, which easily causes illumination light source loss.